Plume‐Induced Delamination Initiated at Rift Zones on Venus

• Published in: Journal of geophysical research. Planets 2023-10, Vol.128 (10), p.n/a
• Main Authors: Adams, Andrea C., Stegman, Dave R., Mohammadzadeh, Hiva, Smrekar, Suzanne E., Tackley, Paul J.
• Format: Article
• Language: English
• Subjects: Buoyancy; Delamination; Evolution; Lithosphere; Mathematical models; Modelling; Numerical models; Planetary mantles; Plates (tectonics); Plume models; Recycling; Rift zones; Subduction (geology); Tectonics; Thickness; Thin plates; Trenches; Two dimensional models
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2023JE007879

Venus' tectonic evolution is not well understood. Thousands of kilometers of possible subduction sites on Venus have been identified along networks of rift zone trenches called chasmata. Rift zones are strong candidates for tectonic recycling due to pre‐existing weaknesses in the lithosphere. Recently, peel‐back delamination (PBD) was proposed as a mechanism of regional‐scale lithospheric recycling initiated at Venusian rift zones (Adams et al., 2022, https://doi.org/10.1029/2022je007460). PBD occurs when the lithospheric mantle becomes sufficiently thick and negatively buoyant to decouple and peel away from the overlying crust remaining at the surface. Both positively and negatively buoyant lithosphere were shown to undergo buoyancy‐driven PBD, though delamination is inhibited by increasing positive plate buoyancy. In this study, we use 2D numerical models to verify that delamination can be initiated in thinner, more positively buoyant lithosphere than in models with no plume‐rift interactions. Our results show that plume‐induced PBD in positively buoyant plates is facilitated by the excess negative buoyancy in the lithospheric mantle and increasing plume buoyancy force, and it is inhibited by increasing crustal buoyancy and decreasing rift width. We propose an age‐progressive framework for delamination at rift zones, where young, thin plates require a larger plume buoyancy force to be destabilized than thicker, yet still positively buoyant plates. We use lithospheric thickness constraints to predict PBD may be most likely to initiate near the Dali‐Diana Chasmata system. Plain Language Summary Venus' tectonic evolution is not well understood. Long networks of rift zone trenches called chasmata have previously been identified as potential locations of tectonic recycling due to their pre‐existing lithospheric weaknesses. Peel‐back delamination (PBD) was recently proposed as a potential mechanism of regional‐scale lithospheric recycling on Venus, in which dense, trench‐adjacent lithospheric mantle detaches and “peels away” from the overlying layer of buoyant crust remaining at the surface. In this study, we use 2D numerical models to further investigate the conditions in which delamination may operate in chasma rift zone environments on Venus by considering complexities from plume‐rift interactions. We find that increasing plume radius, and thereby buoyancy force, results in PBD events in increasingly positively buoyant lithosphere compared to non‐plume mode